Metabolic bone disease in preterm newborn or osteopenia of prematurity (OP), or neonatal rickets or rickets of prematurity, are terms used to describe a common and significant problem that refers to hypo-mineralized skeleton of premature infants that is hallmarked by radiographic evidence of decreased bone mineralization and often leads to fractures of long bone and ribs. In an effort to maximize bone mineralization and minimize OP, clinicians use biochemical measurements of serum calcium, inorganic phosphorus, and alkaline phosphatase to make decisions for optimizing infant nutrition, but are limited to radiographic evidence over time to monitor this progress. Currently, no screening test has been shown to provide both sensitive and specific evidence of developing OP over the first several weeks of life in the premature infants. Such information would greatly facilitate clinicians? efforts to optimize nutrition for preterm infants in an effort to minimize the risk of OP. Current bone assessment tools include plain radiography, dual-energy X-ray absorption (DXA), and quantitative ultrasonography (QUS). Due to the use of ionizing radiation and bulky equipment, the first two methods are not suitable for infants and especially for the low-birth-weight pre-term neonates, a group at particular risk of mineral compromise. QUS is designed to measure the speed of sound in large extremity bones by transmitting a single-frequency ultrasound. Adaptation of this device to infants and especially premature infants is very poor. The most important shortcoming of conventional QUS for evaluation of infant bone is that the results are greatly affected by subcutaneous tissues, particularly by the subcutaneous fat layer. Another shortcoming of the current QUS technology is that the system operates on a single- frequency basis. Based on our investigations, to be described later in this application, acquiring ultrasound data in a wide range of frequencies, especially in the kilo-Hertz range, can provide valuable information about the mechanical structure of bone and may lead to improved bone assessment. The goal of the proposed project is to develop a new ultrasound based technology, called vibro-acoustic analysis (VAA), which is based on a fundamentally new mechanism that allows evaluation of infant bone properties in a wide frequency range without the interference from subcutaneous tissues. In Aim 1, optimization of the VAA method for quantitative assessment, we will optimize and validate the technique for in vivo study. In Aim 2, we will determine the efficacy of the VAA method for quantitative assessment of tibia bone in a pilot study.The proposed technique will be tested on term and preterm infants to detect and monitor the treatment in a longitudinal study. The technology to be developed in this project may provide clinicians with valuable information to monitor and treat developing OP at a stage where radiographic evidence is not yet apparent. Additionally, quantitative measurements over time using improved VAA technology may facilitate assessments of treatment efficacy, thus further guiding clinical interventions with the strong potential for improved patient outcomes.